Synchronous motor

ABSTRACT

A synchronous motor includes a stator with a stator winding, and a rotor on which magnetic poles made of permanent-magnetic material are formed, each pole having a cambered outer contour, especially an outer contour cambered radially outwards, in particular, 2×p individual poles being salient in the circumferential direction, p being the number of pole pairs.

FIELD OF THE INVENTION

The present invention relates to a synchronous motor.

BACKGROUND INFORMATION

In the case of a rotor of a synchronous motor, it is well-known to use apunch/stacked laminated core, at whose outer surface permanent magnetsare provided.

SUMMARY

Example embodiments of the present invention provide a synchronous motorwhich is easy to control.

According to example embodiments of the present invention, a synchronousmotor has a stator having a stator winding, and a rotor on whichmagnetic poles made of permanent-magnetic material are formed, each polehaving a cambered outer contour, especially an outer contour camberedradially outwards,

in particular, 2×p poles, e.g., especially individual poles, beingsalient in the circumferential direction, p being the number of polepairs.

This has the advantage that in the case of one pole of a pole pair, thepermanent magnets are disposed so as to be magnetized radially outwards,and in the case of the other pole of the pole pair, are disposed so asto be magnetized radially inwards. In addition, because each pole iscambered radially outwards, exceptionally reduced cogging torque isachievable, resulting in an electromotive system particularly easy tocontrol.

To be understood by the term camber in this context is that therespective pole has an outside diameter increasing in thecircumferential direction from its first pole edge up to its other poleedge and then decreasing again. In this connection, it is true that thepermanent-magnetic material of a pole may be realized in one piece andtherefore cambered and, in the process, smoothly curved. However, it ispainstaking and therefore costly to produce such a one-piece, cambered,permanent-magnetic body. Alternatively, the cambered structure may alsobe realized using individual permanent magnets, the centers of massand/or midpoints of the permanent magnets being disposed along animaginary cambered line. Preferably, the line is a segment of a circulararc. Thus, in the case of cuboidal permanent magnets, a camberedimaginary line is also present, which in each instance connects at leastone edge of each permanent magnet. Preferably, this line is also acircular-arc segment.

To realize the camber, an outer-surface segment of one permanent magnetis disposed at a greater or smaller radial distance than thecorresponding outer-surface segment of a permanent magnet of the samepole directly adjacent in the circumferential direction. The camber isthus realized in discrete fashion.

The circumscribing radial distance of the outer surface of therespective pole may decrease in the circumferential direction from themiddle of the pole, especially up to the pole edge lying outside in thecircumferential direction, in particular, the circumscribing circlebeing that which does not cut, but rather only touches the permanentmagnets, thus, has only one or two points of intersection with therespective permanent magnet. This is advantageous because an easilyproducible circular camber is thus able to be realized.

Each pole may have two or more permanent magnets, in particular, thepermanent magnets being substantially identical, each permanent magnetin particular being cuboidal. The advantage is that an especially simplemanufacture is feasible, since cuboidal permanent magnets may beproduced easily and cost-effectively. To produce the pole, the permanentmagnets thus only have to be bonded on suitably even surface sections ofthe laminated core, the laminated core being formed such that the camberof the pole is achieved, even though the permanent magnets are cuboidaland substantially identical.

The permanent magnets may be disposed on a laminated core made ofstacked individual laminas, in particular each permanent magnet beingmounted on a flat surface section of the laminated core and bonded toit, the surface element extending in the stack direction andtransversely to it. This offers the advantage of permitting a simplemanufacture. In particular, adhesive bonding of the permanent magnets tothe laminated core is easily practicable.

The slot number N₁ of the stator may be selected such that theinequationα_(P) ×N ₁≠2×p×N _(M)is satisfied, in which αP is the pole pitch, p is the number of polepairs and N_(M) is the number of permanent magnets per pole. This offersthe advantage that cogging torque due to the slotting and/or poles maybe reduced. Thus, torque ripple is reduced and the synchronous motor isbetter able to be controlled.

The camber may have a camber radius R_(pa) which is more sharply curvedthan the radius D_(i1)/2 of the receiving opening in the stator, inparticular so that the following applies:R _(pa) <−δ+D=/2,in which δ is the air gap between the maximum outside radius of therotor and the minimum inside radius of the mounting opening in thestator for accommodating the rotor and D_(i1) is the diameter of themounting opening in the stator for accommodating the rotor. Theadvantage in this context is that the pole is cambered, thus, has asharper curvature than a circle, whose midpoint lies on the rotor axisand whose radius touches the point of the pole surface lying at thegreatest radial distance.

The following may apply for the pole pitch:

0.8≦α_(P)≦0.85. This offers the advantage that again, the cogging torqueand torque ripple of the synchronous motor are reducible.

The maximum air gap, occurring at the pole edges, between the pole andthe mounting opening may be selected such that the following applies:2×δ≦δ_(max)≦3×δ,particularly so that the camber thus extends radially over less thandouble the air gap, but at least over a radial-distance areacorresponding to the air-gap distance. This is advantageous becausecogging torque due to the slotting is again reducible.

In the axial direction, the pole may have two substantially identicalsections, between which there is an offset in the circumferentialdirection that amounts to an offset angle of 180°/KGV (N₁, 2×p), inwhich

KGV denotes the smallest common multiple,

N₁ denotes the stator slot number and

p denotes the number of poles. This is advantageous because torqueripple and cogging torque of the synchronous motor due to the slottingare reducible.

The stack direction of the laminated core may be the axial direction.This is advantageous because the flat joining surface is able to beproduced by adhesive agent which clings, as it were, in surfaceroughness present in the stack direction. In this manner, the joiningstrength is able to be increased.

The poles may have a continuous or discretely approximate angle ofinclination in the axial direction. This has the advantage that torqueripple and cogging torque of the synchronous motor due to the slottingare reducible, and in turn, improved controllability of the synchronousmotor is thus attainable.

It should be understood that present invention is not limited to thefeature combination described below. Further beneficial combinationpossibilities of features of the specification and/or of the figuresshould become apparent from the following discussion for one skilled inthe art.

Example embodiments of the present invention explained in greater detailbelow with reference to FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows the rotor of a synchronous motor, the rotor shaft able tobe accommodated in a central opening 9 being left out.

Disposed on the rotor shaft, which is insertable in opening 9, is alaminated core 7 that is made up of joined individual laminas,preferably punch/stacked and/or welded.

Permanent magnets (1, 2, 3, 4, 5, 6) are disposed at the outercircumference of laminated core 7, one magnetic pole being formed from aplurality of permanent magnets (1, 2, 3, 4, 5, 6). In FIG. 1, each poleis formed of six permanent magnets (1, 2, 3, 4, 5, 6).

In each case gaps are located between the poles in the circumferentialdirection.

With the aid of the multi-piece construction of a pole, thus, theformation of each pole from six permanent magnets (1, 2, 3, 4, 5, 6),eddy-current losses are reduced.

Permanent magnets (1, 2, 3, 4, 5, 6) are magnetized in the radialdirection.

Each pole has a maximum outside radius, which is centrally located inthe angular range of the pole in the circumferential direction.

From the circumferential position of the maximum outside radius up tothe respective gap adjoining the pole, the outside radius of the poledecreases. The outer envelope curve of the pole is thus cambered on bothsides in the circumferential direction.

In this context, each pole is made up of six individual permanentmagnets, which are adhesively bonded on the laminated core. Eachpermanent magnet is cuboidal and is stuck on a flat outer surface oflaminated core 7 provided specifically for it. The radial outer surfaceof laminated core 7 is thus polygonal in the area of the pole in across-section, the normal to the sectional plane being aligned in theaxial direction, in the respective flat area of the polygon, an adhesivesurface extending in the axial direction.

The number of permanent magnets per pole is thus N_(M)=6. The rotor hasthe number of pole pairs p=3, thus, 2×p=6 individual poles at thecircumference of the rotor.

The stator slot number N₁ is selected such that the inequationα_(P) ×N ₁≠2×p×N _(M)is satisfied. Thus, cogging torque due to the slotting is as little aspossible.

The rotor is disposed in the stator, the opening in the statoraccommodating the rotor having a diameter D_(i1). At least one air gap δexists between the opening and the rotor. The air gap is minimal at themaximum radius of the pole, thus has the value δ at that location.

The radius R_(pa) circumscribing the camber is selected such that thefollowing applies:R _(pa) <−δ+D _(i1)/2.

The camber, thus the curved profile, of the pole in the circumferentialdirection is thus more sharply curved than the circumference of therotor. Therefore, the outside radius decreases from the center of thepole in the circumferential direction up to the pole edges.

That is why air gap δ in the area of the pole edges which adjoin thegaps assumes a maximum value δ_(max).

Especially low cogging torques are obtained if the followingdimensioning conditions are satisfied:0.8≦α_(P)≦0.85and2×δ≦δ_(max)≦3×δ.

With the aid of the arrangements described herein, substantiallyidentical cuboidal permanent magnets are always usable as permanentmagnets, permitting easy manufacture of the rotor.

To accommodate the rotor shaft, laminated core 7 has a centrally locatedopening 9 for the rotor shaft, and additionally, has openings 8 forreducing the moment of inertia, openings 8 being centrally locatedrelative to the poles in the circumferential direction and being evenlyspaced from each other in the circumferential direction.

Openings 8, set apart uniformly from each other in the circumferentialdirection, are provided in the laminated core of the rotor to reduce themoment of inertia, their maximum extension in the radial direction ineach case being located in the center, determined in the circumferentialdirection, of a respective assigned pole, the number of poles beingequal to the number of openings 8, the radial extension of openings 8 inthe circumferential direction extending symmetrically relative to therespective pole center determined in the circumferential direction, thecross-section of a respective opening 8 corresponding to a rounded-offtriangle. Thus, an advantageous profile is achieved not only for themoment of inertia, but also for the magnetic flux.

In order to further reduce cogging torque, in the axial direction, asubstantially identical construction of the rotor is provided which,however, has an offset in the circumferential direction. In thiscontext, advantageously an offset of the poles with an offset angle of180°/KGV(N₁, 2×p) is selected, KGV denoting the smallest commonmultiple, particularly of N1 and the number of poles. In furtherrefinement, other surface-mounted parts set apart axially may also beprovided which have a specific offset angle relative to each other, orcorresponding surface-mounted parts having a continuous angle ofinclination are also permitted. In the case of the discreteimplementation, each axially subsequent area is in a position rotated inthe circumferential direction by an offset angle relative to the areapreceding it axially.

LIST OF REFERENCE SYMBOLS

-   1 permanent magnet of the first pole-   2 permanent magnet of the second pole-   3 permanent magnet of the third pole-   4 permanent magnet of the fourth pole-   5 permanent magnet of the fifth pole-   6 permanent magnet of the sixth pole-   7 laminated core-   8 opening for reducing the moment of inertia-   9 opening for accommodating the rotor shaft-   R_(pa) radius circumscribing the camber of the pole-   δ air gap-   δ_(max) maximum air gap-   N_(M) number of permanent magnets per pole-   p number of pole pairs-   N₁ stator slot number-   α_(P) pole pitch

What is claimed is:
 1. A synchronous motor, comprising: a stator havinga stator winding; a rotor including magnetic poles formed ofpermanent-magnetic material; wherein each pole has a cambered outercontour, circumscribing the permanent-magnetic material and camberedradially outwardly; wherein the pole, in an area of the cambered outercontour, has a local maximum radial distance as a function of an angleat circumference, such that each pole has a maximum radial distance thatis greater than a maximum radial distance of the rotor in anangle-at-circumference area between two poles immediately adjacent inthe circumferential direction; and wherein 2×p poles are salient in thecircumferential direction, p being the number of pole pairs.
 2. Thesynchronous motor according to claim 1, wherein the circumscribingoutside radius of the respective pole decreases in the circumferentialdirection from the center of the pole, up to the pole edge lying outsidein the circumferential direction, wherein the circumscribing radius is aradius that does not cut, but rather only touches the permanent magnets,and has only one or two points of intersection with the respectivepermanent magnet.
 3. The synchronous motor according to claim 1,wherein: each pole has at least two permanent magnets, all permanentmagnets of all poles are substantially identical geometrically; thepermanent magnets are magnetized differently; and/or each permanentmagnet is cuboidal.
 4. The synchronous motor according to claim 1, thepermanent magnets are arranged on a laminated core made of stackedindividual laminas, each permanent magnet being mounted on a flatsurface section of the laminated core and bonded to it, the surfaceelement extending in the stack direction and transversely to it.
 5. Thesynchronous motor according to claim 1, wherein a slot number N₁ of thestator satisfies the relationship:α_(P) ×N ₁≠2×p×N _(M) in which α_(p) represents a pole pitch, prepresents a number of pole pairs, and N_(M) represents a number ofpermanent magnets per pole.
 6. The synchronous motor according to claim1, wherein the camber has a camber radius R_(pa) which is smaller than aradius D_(i1)/2 of a mounting opening in the stator, and the camber ismore sharply curved than the mounting opening in the stator, such thatthe following relationship is satisfied:R _(pa) <−δ+D _(i1)/2, in which δ represents an air gap between amaximum outside radius of the rotor and a minimum inside radius of themounting opening in the stator for accommodating the rotor and D_(i1)represents the diameter of the mounting opening in the stator foraccommodating the rotor.
 7. The synchronous motor according to claim 5,wherein the following relationship is satisfied for pole pitch0.8≦α_(P)≦0.85.
 8. The synchronous motor according to claim 6, wherein amaximum air gap, occurring at pole edges, between the pole and amounting opening satisfies the following relationship:2×δ≦δ_(max)≦3×δ, so that the camber extends radially over less thandouble the air gap.
 9. The synchronous motor according to claim 1,wherein, in the axial direction, the pole has two substantiallyidentical sections, between which is an offset in the circumferentialdirection that amounts to an offset angle of 180°/KGV(N₁,2×p), in whichKGV represents a smallest common multiple, N₁ represents a stator slotnumber, and p represents the number of poles.
 10. The synchronous motoraccording to claim 1, wherein a stack direction of a laminated core isthe axial direction.
 11. The synchronous motor according to claim 1,wherein the poles have a continuous or discreetly approximate angle ofinclination in the axial direction.
 12. The synchronous motor accordingto claim 1, wherein a first, non-trivial, non-vanishing order of amultipole expansion of a cross-section of the rotor corresponds to thenumber of poles of the rotor.
 13. The synchronous motor according toclaim 1, wherein a first, non-trivial, non-vanishing order of themultipole expansion of a cross-section of the rotor corresponds to thenumber of poles of the rotor, and/or a first, non-trivial,non-vanishing, higher magnetic multipole moment of the rotor correspondsto the number of poles of the rotor.
 14. The synchronous motor accordingto claim 1, wherein a radial distance of the outer contour of the rotoris a non-constant, periodic function of an angle at circumference, anumber of local maxima of the function corresponding to the number ofpoles at the circumference of the rotor.
 15. The synchronous motoraccording to claim 1, wherein openings, set apart uniformly from eachother in the circumferential direction, are provided In a laminated coreof the rotor to reduce the moment of inertia, a maximum extension in theradial direction in each case being located in a center, determined inthe circumferential direction, of a respective assigned pole, a numberof poles being equal to a number of openings, a radial extension of theopenings in the circumferential direction in particular extendingsymmetrically relative to the respective pole center determined in thecircumferential direction, a cross-section of a respective openingcorresponding to a rounded-off triangle.